I hate that social factors like popularity are a thing in technical decisions.
I have not used mercurial (though heard good things about it) but I saw a similar thing play out in Rust gamedev. There are 2 competing game engines, one better technically, the other much more popular. Now, if everyone made a purely technical decision, they'd pick the first one and eventually it would become the more popular one. Unfortunately, whenever I asked people why they chose the second one, they said because it was more popular. Tragedy of the commons.
If it's any consolation, maybe jj will take over. I haven't tried it yet (I use the staging area a lot in my workflow), but AFAIK they made the choice to be git-compatible which means it's not a choice between one or the other but lets people and teams migrate gradually.
FWIW you can still have a staging-area-like workflow with JJ - it's just that while git has "commits", "the staging area", "the working directory", and "stashes" as four separate concepts with four separate toolkits, in JJ all of those things are "commits" and a single toolkit works with all of them :)
> Tragedy of the commons
That's a different concept. You are describing network effects.